Auto FP High Speed Sync mode - Nikon F6 + SB-800 flash

I stuck the following on a Nikon mailing list, but I thought I'd try
here too.

Hi,
I have an F6 and in the instructions it says you can use high shutter
speeds (up to 1/8000th sec) in "Auto FP High Speed Sync mode" if used
with an SB-800 (perhaps some other speedlights too, but definitely the
SB-800).

Well I have the SB-800 and the F6. If I set the flash mode to 1/250FP as
it says in the F6 manual, I can set the shutter speed to anything I
want. But as soon as the SB-800 is attached, so the indicated speed
drops to 1/250. The SB-800's manual says these high speed modes must be
set on the camera, not on the flashgun.

Also, reading the SB-800's manual, it says the duration of the flash is
as follows:

1/1050 at M 1/1 (full output)
1/1100 sec at M 1/2 output.
1/2700 sec at M 1/4 output
1/5900 sec at M 1/8 output
1/10900 sec at M 1/16 output
....
1/41600 sec at M 1/128 output

So it seems to me that unless the output is somewhere between 1/8th and
1/16th of full output (or less), the length of the flash will be
1/8000th of second, so it seems unlikely you could ever use 1/8000
except perhaps at very close distances. But I can't get the shutter
speed to indicate anything faster than 1/250th, no matter what I do. I
even changed the ISO of the film as if I was rating it at some huge ISO
(whatever the maximum supported on the F6 is), but still no joy. I thied
this on an 20mm f/2.8 and the 70-200 f/2.8 VR lenses.

It's probably me reading the manual wrong, as my last Nikon was an F3
which was ever so slightly (well quite a lot really) less complex than
the F6. And the SB-800 is a pretty complex bit of kit too.

BTW, does anyone know why the duration of the flash differs so little
(1/1050th vs 1/1100th sec) going between full and half output? At
anything under 1/2th output, the duration gets much shorter, but above
that, the duration remains the same. I'm just interested in how they
control the output level. (This is my science/engineering background
being inquisitive).

dave

For my D1H , you just set the mode to M [manual] set the desired shutter
speed n aperture,
set the SB-80DX speedlight mode to M ... then adjust the power til it
indicates FP.

Then flash away

=bob=

"Dave" wrote in message ...
I stuck the following on a Nikon mailing list, but I thought I'd try here
too.

Hi,
I have an F6 and in the instructions it says you can use high shutter
speeds (up to 1/8000th sec) in "Auto FP High Speed Sync mode" if used with
an SB-800 (perhaps some other speedlights too, but definitely the SB-800).

Well I have the SB-800 and the F6. If I set the flash mode to 1/250FP as
it says in the F6 manual, I can set the shutter speed to anything I want.
But as soon as the SB-800 is attached, so the indicated speed drops to
1/250. The SB-800's manual says these high speed modes must be set on the
camera, not on the flashgun.

For my D1H , you just set the mode to M [manual] set the desired shutter
speed n aperture,
set the SB-80DX speedlight mode to M ... then adjust the power til it
indicates FP.

Then flash away

=bob=

"Dave" wrote in message ...
I stuck the following on a Nikon mailing list, but I thought I'd try here
too.

Hi,
I have an F6 and in the instructions it says you can use high shutter
speeds (up to 1/8000th sec) in "Auto FP High Speed Sync mode" if used with
an SB-800 (perhaps some other speedlights too, but definitely the SB-800).

Well I have the SB-800 and the F6. If I set the flash mode to 1/250FP as
it says in the F6 manual, I can set the shutter speed to anything I want.
But as soon as the SB-800 is attached, so the indicated speed drops to
1/250. The SB-800's manual says these high speed modes must be set on the
camera, not on the flashgun.

Dave wrote:

I stuck the following on a Nikon mailing list, but I thought I'd try
here too.

Hi,
I have an F6 and in the instructions it says you can use high shutter
speeds (up to 1/8000th sec) in "Auto FP High Speed Sync mode" if used
with an SB-800 (perhaps some other speedlights too, but definitely the
SB-800).

Well I have the SB-800 and the F6. If I set the flash mode to 1/250FP as
it says in the F6 manual, I can set the shutter speed to anything I
want. But as soon as the SB-800 is attached, so the indicated speed
drops to 1/250. The SB-800's manual says these high speed modes must be
set on the camera, not on the flashgun.

Also, reading the SB-800's manual, it says the duration of the flash is
as follows:

1/1050 at M 1/1 (full output)
1/1100 sec at M 1/2 output.
1/2700 sec at M 1/4 output
1/5900 sec at M 1/8 output
1/10900 sec at M 1/16 output
...
1/41600 sec at M 1/128 output

So it seems to me that unless the output is somewhere between 1/8th and
1/16th of full output (or less), the length of the flash will be
1/8000th of second, so it seems unlikely you could ever use 1/8000
except perhaps at very close distances. But I can't get the shutter
speed to indicate anything faster than 1/250th, no matter what I do. I
even changed the ISO of the film as if I was rating it at some huge ISO
(whatever the maximum supported on the F6 is), but still no joy. I thied
this on an 20mm f/2.8 and the 70-200 f/2.8 VR lenses.

High speed flash is spread out in little pulses (unlike normal flash which is an
uncontrolled discharge up to the point where the TTL shuts it off.)

High speed flash: http://www.photozone.de/bindex3.html

For 'normal flash', the discharge curve goes from 0 to full power very quickly,
so for the lowest power, the flash has to be stopped before full discharge rates
occur. That is why a plot of the timings above is so skewed. Here is a link
for both high speed and TTL flash.

http://www.chem.helsinki.fi/~toomas/...flash-faq.html
http://www.chem.helsinki.fi/~toomas/...discharge.html





It's probably me reading the manual wrong, as my last Nikon was an F3
which was ever so slightly (well quite a lot really) less complex than
the F6. And the SB-800 is a pretty complex bit of kit too.

BTW, does anyone know why the duration of the flash differs so little
(1/1050th vs 1/1100th sec) going between full and half output? At
anything under 1/2th output, the duration gets much shorter, but above
that, the duration remains the same. I'm just interested in how they
control the output level. (This is my science/engineering background
being inquisitive).

See the link above. Will answer much.

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